Method and device for testing aldehyde in polyester polymer

ABSTRACT

A test strip, methods for making and using the test strip, and a kit are described, which allow for the simple and efficient determination of the acetaldehyde content in a polyester polymer. The strip and methods have application, for example, in the manufacture of polyethylene terephthalate preforms and containers, where existing methods for testing for acetaldehyde are cumbersome and time consuming.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to methods for testing aldehyde inpolyester polymers using an aldehyde-sensitive indicator. The inventiveindicator is capable of detecting acetaldehyde (AA) in the microgramrange.

[0003] 2. Summary of the Prior Art

[0004] During melt molding of polyethylene terephthalate (PET), such asinjection molding a preform and extrusion molding a parison forpackaging containers, AA is generated as a by-product due to the thermaldegradation of the PET polymer. The AA formed is trapped within themolded preform or parison and packaging container made therefrom.Ultimately, the entrained AA diffuses gradually from the container wallinto the liquid/beverage contained therein. If present in sufficientquantities, the migrated AA can impart a sweet fruity-like odor andflavor to the product, thereby affecting its perceived quality. Thesensory detection threshold of AA in water has been reported to be 20 to40 μg/L levels in water. The odor detection thresholds in carbonatedsoft drinks are expected to be much higher because of the masking effectof other ingredients.

[0005] The amount of AA generated depends greatly on the heating timeand temperature experienced by the polymer during the molding process.Accordingly, AA testing is an important quality assurance procedure forPET preforms/bottles manufacturing to ensure that the finishedcontainers are within the acceptable AA specification.

[0006] Currently, two methods are used in the industry for determiningAA in PET: ground parison (GPAA) and headspace (HSAA) methods. The GPAAmethod entails cooling preforms or resin pellets in liquid nitrogen andgrinding them in a mill to form powders (typically less than 1 mm insize). The PET powder is then weighed into an airtight headspace vialand heated to 140-160° C. for 60-90 min. Following the heating process,the AA collected in the headspace is sampled and analyzed using a gaschromatograph (GC). The concentration of AA in the PET is typicallyexpressed as ppm (one part AA per one million part PET by weight).Typical acceptable GPAA values can range 8-25 ppm of PET.

[0007] The HSAA method involves measuring the amount of AA diffused intothe headspace of an unfilled bottle after conditioning the bottle at22-25° C. for 24 h after blow molding a preform to form a bottle. The AAconcentration of the headspace air is determined by sampling a portionof the bottle headspace and analyzing the headspace sample with a GC.This is typically performed automatically using an auto-sampling system.A typical upper limit of GPAA value is in the range of 4-5 mg/L AAconcentration of the bottle headspace.

[0008] The GPAA method measures residual AA in the PET preform, and thusis a direct measurement of AA content in the PET sample. The HSAA methodprovides only an indication on the AA content for the PET bottle, as theAA test results which are dependent on the size/shape, stretch ratio,crystallinity, conditioning time/temperature and other parameters forthe container. Preform makers, blow molders and end users haveestablished GPAA and HSAA values that should not be exceeded to assurethat the residual AA does not affect the perceived quality of the liquidproduct significantly. Although the HSAA and GPAA methods are currentlyaccepted by the industry for evaluating AA in PET, these tests arelaborious and time-consuming. Moreover, the test instruments areexpensive, complicated, and require a specially trained individual tooperate the equipment.

[0009] In search of a faster, easier and more cost-effective method, theinventors herein have developed the disclosed aldehyde indicatortechniques. Indicator strips have been used extensively for detectingand quantifying compounds in various areas ranging from clinical fieldsto food industries. In general, these tests are characterized by theirsimplicity, which consists of exposing an indicator strip to the testsample and reading the results. These indicators are, in general, madeof an adsorbent or carrier impregnated with the reagents that aresensitive to the compound of interest. There have been several methodsand related procedures developed for determining aldehydes. Each ofthese known methods contains some disadvantage causing them to be lessthan optimal. For example, U.S. Pat. No. 4,511,658 describes a method ofapplying a ketone solution of4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT, trademark name“Purpald” from Aldrich Chemical Co. Milwaukee, Wis.) on inert solidsupport coated with a metal bicarbonate (e.g., NaHCO₃ or KHCO₃). Thecolorimetric detector is said to be highly selective to formaldehyde,and therefore precludes its use for testing other aldehydes, includingAA. U.S. Pat. No. 5,128,171 disclosed a methodology for preparing a teststrip comprises a support and a reagent layer consisting of a dialyzedlatex polymer (e.g., carboxylated vinyl acetate/ethylene copolymer),3-methyl-2-benzothiazolinone hydrazone (MBTH) and other compounds. Itclaims that by using a dialyzed polymer in the reagent layer, theresulting test strip maintains its integrity for a substantially longertime as compared to using an undialyzed polymer. While the use of thisstrip may be suitable for testing liquid samples, its use in testing AAin air may be less effective because AA needs to permeate into the latexmatrix and react with the reagents contained therein. U.S. Pat. Nos.3,645,696 and 3,784,358 describe methods to stabilize a chromogenicreagent for use in the indication of ethylene glycol antifreezecontamination in crankcase oil. The patents describe applying MBTH onsolid supports (silica gel or porous polyethylene) and drying innitrogen gas. This method is intended for testing aldehydes in oiland/or liquid medium, but it is not optimal for testing AA in air. Inaddition, when a transmission measurement of the colored solution isused for achieving the desired test sensitivity, the chromogen formed onthe solid support tends not to dissolve easily in the oxidizingsolution. Another U.S. Pat. No. 4,438,206 discloses a method to improvethe test sensitivity of acetylacetone by adding a serum albumin to thesolution. However, as noted by the inventors, the enhancement offluorescence intensity by addition of the serum albumin is achievableonly in the reaction of the acetylacetone with formaldehyde, but not AA.

[0010] Many commercial products are also available for testing aldehydecompounds in air which involve passing the test air through a cartridge,tube or badge containing aldehyde-sensitive reagents. These devicesrequire a large volume of air, long exposure time, or further desorptionand separation treatment upon reaction, which render them unsuitable fortesting AA in limited headspace air for PET samples.

[0011] In a PET preform/bottle production environment, it is importantto identify quickly a deviated process as it occurs to reduce scrap andminimize the production cost. Therefore, it is of great benefit to havean AA test method that can be performed routinely, rapidly,cost-effectively and simply enough for use by the operator of a moldingmachine without involving a complicated analytical technique. Thisinvention describes such a test process involving the aldehyde-indicatortechnique for quantitative and semi-quantitative testing of AA in PETpolymer.

SUMMARY OF THE INVENTION

[0012] The invention is embodied in an aldehyde indicator for detectingaldehyde in a gaseous medium which has been extracted from a sample ofpolymer. The strip includes an aldehyde-reactive reagent coated on acarrier. A thin layer of the coated carrier is applied to a tape whichis non-reactive with the aldehyde-reactive reagent. The tape may beanchored to a support so that the indicator can be handled withoutcontacting the reagent. The carrier may also be adhesively bonded to thesupport, or physically immobilized to the support. In preferredembodiments the aldehyde-reactive reagent is3-methyl-2-benzothiazolinone hydrazone (MBTH). The concentration of theMBTH is preferably between 0.5 to 3% by weight.

[0013] The invention is also embodied as a method for using an indicatorto detect AA in a gaseous medium, including (1) extracting gaseous AAfrom a solid polyester polymer into a confined space, (2) reacting thegaseous AA with an aldehyde-reactive reagent on a solid particulatecarrier on the indicator, (3) contacting the aldehyde-reactive materialwith an oxidizer solution to obtain a color change in the oxidizersolution, and (4) measuring the color change to correlate the reactedacetaldehyde. Preferred embodiments described herein detail how AA canbe extracted from PET by heating the preform at elevated temperature,how to optimize the color change reaction by modifying the oxidizer, andthe best reagents and carriers to use. The oxidizer solution, or reagentsolution, may be an aqueous solution of ferric chloride, potassiumferricyanide, lead tetraacetate, periodic acid, or acidified ferricchloride. Preferably the ferric chloride solution is between 05. to 3%by weight. The reactive reagent may be coated on a corner applied to asupport strip.

[0014] The solvent for forming the solution of aldehyde-reactive reagentmay be water, or an organic solvent. The pH of the solution is optimizedto promote solubilization of the reagent.

[0015] Different aspects of the invention embodied in the indicator andthe method of using it may be embodied together in a kit for testing forthe quantity of acetaldehyde extracted from a solid polyester polymerinto a gaseous medium. The kit includes: (1) an indicator strip, (2) anoxidizer, and (3) an air-tight-sealable container or closure for cappingthe preform to form a hermetic preform headspace. To use the kit, AA inthe gaseous medium is contacted with the indicator strip in the airtightcontainer or the capped preform. The strip is then contacted with anoxidizer producing a color change. The indicator includes a detectionlimit of at least 0.5 ug of acetaldehyde. The amount of AA detected isthen read by correlating the color change according to a predeterminedrelationship, such as by comparison with a color chart or using aspectrophotometer. Such chart or graph could be provided with the kit orseparately.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic diagram of an indicator according to anembodiment of the invention.

[0017]FIG. 2 depicts an indicator in combination with a capped preformto be tested according to an embodiment of the invention.

[0018]FIG. 3 graphically depicts an example of calibration plot forcorrelating an absorbance measurement with a quantity of acetaldehyde ina sample.

[0019]FIG. 4 depicts a setup to heat preform without deforming theclosure region of the preform according to an embodiment of theinvention.

[0020]FIG. 5 graphically depicts an example of correlation plot tocorrelate AA measured according the invention and AA determined usingthe known ground parison acetaldehyde analysis (GPAA).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The invention relates to a process of determining AA in polyesterpolymers, for example, in PET and polyethylene naphthalate (PEN), usingan aldehyde-reactive indicator as described herein. A polymer part maybe a preform, or a bottle, or a container. The process primarilyconsists of three steps: (1) extraction of AA from the plastic into agaseous medium; (2) reaction of AA with the indicator; (3) treatment ofthe indicator to give a detectable response; and (4) quantification ofthe response.

[0022] Step (1) involves heating the polymer of interest in a closedsystem to increase the rate of AA extraction from the polymer matrix tothe enclosed headspace air. Several methods to achieve this hermeticenvironment include, without limitation, are recited in summary form onTable 1. TABLE 1 Methods of extracting AA from PET Method AA diffusedout from 1 Capping PET preform with a closure. Interior wall of preform2 Capping blown PET bottle with a closure. Interior wall of bottle 3Placing entire preform in an airtight Interior and exterior containerwalls of preform 4 Placing entire bottle in an airtight Interior andexterior container walls of bottle 5 Placing cut-up pieces ofpreform/bottle in Exposed surfaces of an airtight containerpreform/bottle 6 Placing resin pallet in an airtight container Surfaceof pallet 7 Placing preform/bottle/pellet grinds in a Bulk ofpreform/bottle/ sealed container pellet

[0023] Due to the increased internal pressure of the container andpreform during heating, it is important to select an appropriate sealingmechanism to ensure that the seal integrity is not compromised. In usingmethods 1 and 2 in Table 1 for example, the optimal condition may belimited to temperatures below the glass transition temperature of PET(≈75° C.), to prevent a leaky closure caused by thermal softening of thepolymer. If polyolefin closures are used for these methods, the testtemperature will need to be reduced further as increasing thetemperature can cause a considerable softening of these closures. On theother hand, closures made from thermoset phenolic resins tend to offerbetter seal performance, as they do not soften at elevated temperatures.If a higher heating temperature is desired, the leakage may be avoidedby heating only the preform body below the thread finish, for example,by submerging the preform in a heated water bath up to the support ledgeregion.

[0024] In theory, heating the test sample to higher temperatures shouldincrease the rate of AA diffusion to the headspace. As well, underelevated temperature conditions, the solubility of AA in the polymerdecreases, thereby increasing AA concentration in the headspaceimproving test sensitivity. However, when the reagent is heated togetherwith the test sample, excessive heating can compromise the testsensitivity due to thermal decomposition of the aldehyde reagent. It istherefore important to select a heating time/temperature combinationsuitable for the reagent to ensure no significant break down occurs.These conditions can be established easily by those of ordinary skill inthe art through empirical tests.

[0025] Elevated temperature conditions may be unnecessary as long as theamount of AA collected in the enclosed headspace is sufficient forreacting with the strip to provide responses of acceptable sensitivity.If testing at lower temperature, such as ambient temperature, isdesired, an extended test time may be used to increase the amount of AAavailable for reaction.

[0026] To take full advantage of the effect of increased AAconcentration in the headspace under elevated temperature, steps (1) and(2) (i.e., extraction and reaction steps) may be conducted at differenttimes to avoid thermal degradation of the aldehyde reagent. With thisapproach, a mechanism to expose the reagent to the AA-containingheadspace air, without causing leakage for the sealed container, isneeded. One way to achieve this is to adapt a septum on the closure forthe container to allow for a syringe needle to be inserted to the vesselheadspace without affecting the seal integrity of the vessel. A devicethat is intended for solid phase micro-extraction and desorption asdescribed in U.S. Pat. No. 5,691,206 may be suitable for thisapplication. Briefly, the syringe device is made up of a fiber housedwithin a needle. When the plunger of the syringe is depressed, the fiberis exposed to the test gas. To use the device for this application, thefiber will need to be coated with the aldehyde-reactive reagent.

[0027] Another method is to use an airtight syringe equipped with acheck valve for sampling the headspace air. The diameter of the syringebarrel must be large enough to allow the AA indicator strip (referringto FIG. 1 without the handle strip) to lie flat at the end of the barrelwhen the plunger is fully depressed. To test the headspace air, thesyringe needle is inserted through the septum and into the headspace ofthe vessel to withdraw a fixed volume of air into the syringe barrel.This is followed by closing the check valve to prevent the loss of thecollected headspace gas. The sampled headspace air is then allowed toreact with the indicator strip until sufficient AA in the headspace isreacted with the reagent. The headspace sampling is best performed whenthe vessel has been cooled to room temperature to minimize the elevatedpressure effect during heating. Although various types of syringes maybe used, HAMILTON SampleLock (a trade mark) syringe is found to besuitable. The aforementioned techniques are useful in cases where theamount of AA extracted at low temperatures is otherwise too low foraccurate quantification.

[0028] In step (2) of the current invention, the AA extracted from theheadspace reacts with the aldehyde-sensitive reagent present on theindicator. The nature of the reaction may be based on chemical,enzymatic, catalytic, immunogenic or any other form of electrical,chemical or physical activities. Many compounds are known to react withaldehydes to form specific reaction products that can be determinedvisually and photometrically. Compounds that may be used in accordancewith the present invention, include, without limitation:

[0029] 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH),

[0030] 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (trade name Purpaldby Aldrich Chemical Co., Milwaukee, Wis.)

[0031] 2-hydrazinobenzothiazole

[0032] 2,4-dinitrophenylhydrazone

[0033] 5-dimethylaminonaphthalene-1-sulfohydrazide (DNSH)

[0034] 2-diphenylacetyl-1,3-indandione-1-hydrazone (DAIH)

[0035] 2-hydrazinobenzothiazole-4-nitrobenzenediazonium fluoborate

[0036] p-nitrobenzalhydrazone

[0037] 1,3-cyclohexanedione

[0038] 3,5-diaminobenzoic acid

[0039] 5,5-dimethylcyclohexane-1,3-dione

[0040] 2-hydroxycarbazole

[0041] dimedone

[0042] indole

[0043] The sensitivity of the test is dependent on the reactioncharacteristics for the reagent employed, such as the chain conjugationbetween resonance terminals, extra conjugation and straight-linedistance between resonance terminals. Thus, for example, when two molesof AA react with one mole of 3,5-diaminobenzoic acid, poor testsensitivity is resulted. When the reaction involves an equimolarreaction of reagent and aldehyde, such as AA reaction with4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, a moderate sensitivityresults. When two moles of reagent react with one mole of aldehyde andthe conjugation chain is lengthened, such as the reaction of AA withMBTH, a greater sensitivity is expected.

[0044] Depending on the reagent employed, the formation of thedetectable response may be spontaneous upon reacting with the aldehyde,or a second step may be needed for further treating the reactedindicator with other reagents. As a result, steps (2) and (3) describedmay take place concurrently or separately. It is also important torecognize that depending on the reagent employed, the pH condition forreaction may need to be varied to achieve the desired results. Forexample, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole requires analkaline condition to form a visually detectable purple chromogen afterreacting with AA. Conversely, 3-methyl-2-benzothiazolinone hydrazonehydrochloride (MBTH) requires an acidic solution to produce a desirableresult. Optimization of pH for any combination of reaction systems maybe determined empirically and is well within the level of ordinary skillin the art.

[0045] In one embodiment of this invention, 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH), which has been reported to possess goodsensitivity to aldehydes was chosen as the preferred reagent for AAtesting in PET. This compound reacts with aliphatic aldehydes (e.g., AA,formaldehyde, propionaldehyde, butanal, glyceraldehydes) to give a bluecolored chromogen that can be visually detected or quantified using aspectrophotometer. The reaction of MBTH with aldehydes can be summarizedas follows:

[0046] In a first reaction, MBTH reacts with AA to form a colorlessazine. In the second reaction, the remaining unreacted MBTH from thefirst reaction is oxidized by an appropriate oxidizing agent to form acation, which reacts with the azine produced from the first reaction togive a blue colored formazan. Since the formation of the formazanrequires the reaction of azine with a second molecule of MBTH, anadequate amount of MBTH must remain after the first reaction to allowfor the second reaction to proceed. From these relationships, it isclear that in order to obtain an effective meausurement MBTH must be inexcess of the aldehyde. Failure to provide this condition, for example,in a scenario where the test gas contains far greater aldehydes contentthan anticipated, will result in an over depletion of MBTH in the firstreaction, and thereby hamper the full development of color. This couldresult in an under-determination of AA present in the test gas. Toovercome this undesirable effect, a MBTH indicator can be first exposedto the test gas and then together with a second unreacted MBTHindicator, dipped into FeCl₃ solution to develop the color. Using thisapproach, a definite upper detection limit for the indicator can beestablished.

[0047] Typically, the aldehyde indicator is prepared by coating acarrier with a solution containing the reagent necessary for appropriatealdehdye detection. In principle, materials that possess all thefollowing characteristics are suitable to use as the carrier for thealdehyde-sensitive reagent: (1) inert to the reagent; (2) possess largesurface area; (3) the reagent is able to coat on the substrate surfacewithout dislodging easily during handling and testing; and (4) thereacted-reagent dissolves readily in the developing solution. Suitablecarriers for the indicator are alumina, silica gel, glass, kaolin,diatomaceous earth ceramic and synthetic polymers. The physical form forthe carrier can be particle, bead, film, membrane, slab, fiber, sheetand foam. When choosing a carrier for this invention, it is important toconsider its mesh size and porosity which would determine the surfacearea available for coating, as well as the exposed area for reactionwith AA. In accordance with this invention, impermeable particulatecarriers are preferred since it is less likely for the chromogen toentrain in the carrier matrix. Generally, a particle size of at leastgreater than 80 mesh (less than 177 μm) is desirable to providesufficient surface area. The particulate carrier may need to be cleanedby heating to an elevated temperature to remove contaminants that areadsorbed during manufacturing, packaging and storage. For instance,alumina may be heated to 200° C. for an hour to remove the adsorbedcontaminants.

[0048] Referring to FIG. 1, in a preferred embodiment of this invention,the indicator, prepared in the form of a support strip, is made up ofparticulate carrier 4 coated with the aldehyde reagent and adhered to anadhesive tape support 6. The adhesive tape is double sided, withadhesive layer 2 adhering the particulate carrier, and adhesive layer 10anchoring the tape and the carrier to the support 8. An uncoated portionof the support serves as a handle to facilitate the handling of thestrip and to avoid finger contact with the reagent. A typical procedurefor preparing this strip would involve first bonding the plastic handlestrip to one side of a double-coated adhesive tape. The second adhesiveside of the tape is then pressed with moderate pressure against a thinlayer of coated carrier particulates that are spread over a cleansurface, such that the carriers are effectively anchored to the adhesivesurface. Alternatively, the reagent-coated carrier may be applied to asingle-sided adhesive tape and then attached to the non-adhesive side ofthe tape to the support using an adhesive or immobilized physically. Theadvantage of the latter approach is that when an opaque particulatecarrier is used, for example alumina, on a transparent adhesive tape,the surface coverage of the carrier on the tape can be inspected readilyby holding the coated tape against a bright background. A well-coveredtape should be opaque, while a poorly coated tape would exhibit patchesof translucent areas.

[0049] The process of coating the aldehyde reagent to the carrierencompasses dissolving the reagent (typically supplied in a powderysolid format) in a solvent, most commonly, deionized distilled water.The condition of the solvent may need to be adjusted in order tosolubilize the otherwise insoluble solid compound, such as applying heatand altering the pH of the solution. Taking 3-methyl-2-benzothiazolinonehydrazone hydrochloride for example, the preferred reagent in thisinvention, while the compound is insoluble in neutral and alkalinesolutions, it dissolves readily in acidic solution of pH<3.5. Thetypical concentration of MBTH for this invention is about 0.5 to 3% byweight.

[0050] A compound may be soluble under certain pH conditions, but itsstability may be affected. For instance, although4-amino-3-hydrazino-5-mercapto-1,2,4-triazole dissolves readily underhigh pH and requires pH>10 to form a chromogen, the compound tends tobreak down gradually over time under the alkaline condition and losesits sensitivity. Therefore, for this compound, it is desirable that thecompound be exposure to an alkaline condition when it is ready forexposing to AA.

[0051] After an appropriate solution is prepared, it is brought intocontact with the carrier by adding directly to the carrier. Whenparticulate carriers are used in the invention, sufficient reagentsolution should be added to give a workable mass such that a homogeneousmixing is possible using a spatula. Therefore, concentration of thesolution must be adjusted to achieve this condition, as well as toensure that enough reagents are present for reacting with theanticipated maximal amount of AA in the test gas.

[0052] To complete the coating process, a drying step is carried out toremove the solvent. The preferred drying method is vacuum drying since alower temperature can be used for drying as compared to drying underambient atmospheric pressure. This minimizes the risk of thermaldegradation on the reagent and prevents potential contamination from theair. Air-drying in conjunction with heating may also be used, providedthat the air is not polluted with carbonyl compounds (e.g., aldehydesand ketones) that would react with the reagent. Alternatively, a cleanstream of dried gas, such as nitrogen and purified air may be used toblanket the drying carrier to prevent the contamination. In onepreferred embodiment of this invention, although3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) does notform a color product when reacting with ketones and non-aliphaticaldehydes, these contaminant compounds, if present in sufficient amount,could deplete MBTH and may hamper the full development of color. On theother hand, other nitrogen containing compounds react with MBTH to formblue or green chromogens and also should be avoided: aniline,N-alkylanilines, N,N-dialkylaniline, diarylamines, indoles, carbozolesand phenothiazines.

[0053] The particulates should be dried until no clumps are evident andthe particulates are free running. There are a number of ways to supplyheat during drying, including vacuum oven, water bath, heater tape,heater mantle, heater block, infrared lamp and microwave. Preferably, atransparent container, such as one made of glass, is used for drying theparticulates, so that visual inspection of the extent of drying ispossible without breaking the vacuum. Depending on the amount of reagentsolution added, mesh size of the carrier, and the drying setup used, thedrying time can vary from minutes to hours. To provide a more efficientdrying, the particulates may be agitated during drying.

[0054] After drying, the reagent-coated carriers are coated on anadhesive strip, thus providing a large surface area for reacting withthe aldehyde vapor, which helps optimize the test sensitivity and reducethe test time. A double-coated adhesive tape may be used so that oneside of the tape is coated with the reagent carrier, while the othersurface is attached to a plastic strip handle for convenient handling ofthe test strip.

[0055] In step (3) of the AA determination process, the aldehydeindicator, which has been reacted with the AA extracted in step (2), isfurther reacted with a second reagent solution to produce a detectableresponse, such as the formation of a color or fluorescent product on thestrip. When a sufficient volume of the solution is used, the solutioncan further act as a solvent to solubilize the product to form ahomogenous solution.

[0056]FIG. 2 depicts an embodiment of the invention to illustrate howthe strip may be used for testing AA in a polymer part, for example aPET preform. Cap closure 16 is air-tightly sealed onto a preform 12 toform a hermetic headspace 20 (add 20 to show where is the preformheadspace) in which AA is extracted to. The indicator strip 18 insidethe preform is shown with an indicator 14 adhered thereon to which thereagent-coated particles in turn have been applied. After reacting withAA in the preform headspace 20, the indicator strip is removed from thepreform and dipped into an oxidizing agent, ferric chloride solution, toform a chromogen which is readily soluble in water to form a coloredsolution. Other oxidizing agents that may be suitable are potassiumferricyanide, lead tetraacetate and periodic acid. At room temperature(≈22° C.), a visually discernible color response is produced in lessthan 15 min upon dipping the strip in the ferric chloride solution.Without agitation, however, the color intensity of the solutioncontinues to deepen with time and approaches a saturated level after 30min. The time taken to reach the final coloration may be shortened byagitation using a shaker, mixer, rotator, magnetic stirrer or heating inwater/ultrasonic bathes.

[0057] In step (4) of the process, the resulting response is detectedvisually or evaluated instrumentally using radiation measurement devicessuch as colorimeter, spectrophotomer, fluorimeter, radiation counter,and the like. For visually detectable color response, the amount ofaldehyde detected may be determined by comparing the result withstandard solutions or a chart to correlate with a desired unit (e.g.,concentration, weight, equivalent unit, etc.). Similarly, when anelectronic device is used for evaluating the results, a calibrationchart may be used. The measurement methods can further be divided,broadly, into two categories: (1) transmission measurement of thesolution containing the dissolved aldehyde-reagent and (2) directreflectance measurement of the response produced on the indicator. Thetransmission method tends to offer a greater radiation signal asemission from the entire depth of the liquid sample is measured. Inaddition, by increasing the path length of the vial/cuvette during themeasurement, the test sensitivity can be increased. Conversely, thereflectance method only measures emission from the test strip surface,which may limit its use in situations where the aldehyde concentrationof the test gas is high or when qualitative or semi-quantitative resultsare sought.

[0058] In one embodiment of this invention, ferric chloride is used as apreferred oxidizing agent for the formation of the chromogen product.The ferric chloride solution in deionized or distilled water generallyhas a concentration of about 0.5 to 3 percent by weight. The ferricchloride solution, when freshly prepared, is yellow in color. However,during storage, the solution gradually becomes more brownish in colorupon aging. Although this transformation of color does not affect itsefficacy in the oxidation reaction, it is necessary to stabilize thecolor of the ferric chloride solution so that a consistent hue of coloris developed upon the oxidation reaction. This is particularly importantin semi-quantitative tests, where the reacted solutions are to becompared to a printed color correlation chart. To stabilize the color ofthe ferric chloride solution, an appropriate amount of inorganic acid(e.g., hydrochloric acid) may be added to the solution. Depending on theamount of the acid added, the ferric chloride solution could bestabilized to a desired hue of yellowness. This characteristic may beexploited such that when the chromogen is formed in the oxidationreaction, the resulting blue greenish solutions provide the mostdesirable visual color contrast at different aldehyde levels.

[0059] The AA detection system of the invention can be provided in theform of a test kit in a variety of formats. Tests have shown that theshelf-life of the indicator strips made with MBTH is affected byhumidity and light of the storage environment. Therefore, to achieve anoptimal shelf-life, the indicator strips may be individually packaged inlaminated aluminum foil or other opaque high water-barrier polymer filmsor containers. Alternatively, the test strips may be packaged in bulkwithin a high moisture barrier glass vial or aluminum canister that islight protected. To minimize the exposure of unused strips to moisturefrom the air, it is desirable to incorporate a desiccant in the form ofa sachet or other formats in the package to remove moisture that entersthe package during packaging, opening and re-closure. Another componentof the kit would be a pre-measured reagent solution for reacting withthe aldehyde-reactive reagent to produce a detectable response. Thereagent solution can be sealed in disposable vials, cuvettes, tubes andthe likes. Preferably, they should be transparent such that the coloredsolution can be measured directly in the vial using a spectrophotometeror comparable to a chart without having the need of transferring thesolution to a second container. This also helps minimize any error dueto inaccurate transfer of solution.

[0060] Another component of the test kit is a seal. The seal may be aclosure for use on a preform or a bottle to form an airtight space.Alternatively, the seal may be an airtight container for receiving thepreform or bottle.

[0061] Without further elaboration, it is believed that one skilled inthe art, by using the preceding description, can reproduce and utilizethe present invention to its full extent. The following preferredembodiments, therefore are meant to be illustrative and are in no wayintended as limiting the scope of the invention described and claimedherein.

EXAMPLE 1

[0062] This example describes how the AA indicator can be prepared usingalumina as a carrier. 3-methyl-2-benzothiazolinone hydrazonehydrochloride monohydrate (MBTH) and ferric chloride hexahydrate werepurchased from Aldrich Chemical Corporation (Milwaukee, Wis.) and usedwithout further purification. Alumina particulate was obtained fromFisher Scientific Ltd. (Nepean, ON) with mesh size of 80-200.

[0063] A 0.05 g sample of MBTH-HCl was accurately weighed into a cleanglass vial and then added with 6 mL of deionized distilled water. Thecontent was stirred until MBTH-HCl was completely dissolved to form a0.83% (w/v) solution. In another round bottom 1.5 cm i.d. 50 mL glasstube, a 3.5 g sample of alumina particulates was accurately weighted.The glass tube had a threaded finish such that a closure, which wasfitted to a tubing connected to a vacuum pump, can be screwed on toprovide a vacuum environment. To the alumina, 3 mL of the MBTH solutionwas added and thoroughly mixed with a stirrer to ensure all the aluminaparticulates were wetted with the MBTH solution. The glass tube was thencapped and the headspace air was evacuated carefully to preventexcessive boiling by slowly opening the valve at the vacuum line. Theglass tube was then heated in a heater block set for one hour at 40° C.to remove the water. Occasionally, the content of the tube was agitatedand tapped to ensure the contents to break up the clumps. At the end ofheating, the alumina should be non-sticky with no visible clumps. Toprepare the indicator strip, a 30 cm long, 9 mm width adhesive tape (3M,St Paul, Minn.) was cut and laid on a clean piece of paper with theadhesive side up. The MBTH-coated alumina was rough spread to theadhesive surface and then fine spread with the aid of a spatula. Toensure a proper anchorage of the coated alumina to the adhesive layerand a complete surface coverage of the alumina on the tape, the tape wasflipped over and pressed lightly along the tape against a thin layer ofthe MBTH-coated alumina that was spread on the paper. Excess aluminaparticulates were shaken off. To inspect the surface coverage of thetape, the tape was held up against a lighted background; a well-coatedtape should be opaque and homogeneous in appearance, while a poorlycoated one would exhibit translucent patches. The translucent areas canbe “touched up” further by applying more coated alumina. The coated tapewas cut into strips of 6 mm×10 mm size and stored in an airtight,light-shielded glass vial containing a desiccant (Drierite, W. A.Hammond Drierite Co. Ltd., Xenia, Ohio) until use.

EXAMPLE 2

[0064] The indicator strips prepared as in EXAMPLE 1 were tested forsensitivity by exposing to AA in 22 mL hermetic glass vials injectedwith known amounts of AA: 0.4 to 1.5 μL of AA standard of concentration985 mg/L (corresponded to 0.4 to 1.5 μg of total AA injected). Thestrips were heated in the vials at 90° C. for one h, after which, theywere removed from the vial and dipped in freshly prepared 1.6 mL of0.63% (w/v) solution of ferric chloride hexahydrate contained in apolystyrene cuvet (Fisher Scientific Ltd., Nepean, ON; semi-micro, 10 mmpath length). After 30 min of reaction time at room temperature (23°C.), the absorbance values of the resulting solutions were measuredusing a spectrophotometer (Model USB2000; Ocean Optics, Inc., Dunedin,Fla.). As shown in FIG. 3, in the AA range tested, the indicator stripsproduced a linear absorbance response at 600 nm wavelength. Visually,the solutions ranged from pale greenish blue for low AA to deep greenishblue for strips reacted with high amount of AA.

EXAMPLE 3

[0065] This example shows how the final color of the ferric chloridesolution, may be changed to a desired hue by using an inorganic acid.

[0066] A 0.25 g of ferric chloride hexahydrate was dissolved in 40 mL ofdeionized distilled water to form a 23 mM ferric chloride solution. A92.5 μL of 37.5% hydrochloric acid was added. Prior to the addition ofthe acid, the ferric chloride solution was yellow in color. Upon theaddition of the acid, the solution became pale yellow in color, which isstable to long-term storage. In contrast, the ferric chloride solutionthat was not acidified with the acid gradually turned to a brownishsolution.

[0067] The ferric chloride solutions, prepared as such, were tested withthe indicator strips prepared as described in EXAMPLE 1, using the sameprocedures as outlined in EXAMPLE 2. The colors of the reacted ferricchloride solutions after the oxidation reaction are summarized in Table2: TABLE 2 Effect of aging and hydrochloric acid on the color of thefinal solution Ferric chloride solution, 0.8 Color of the reacted mL AAreacted, μg solution Freshly prepared with no 0.28 Pale greenish blueacid 0.56 Greenish blue 0.84 Deep greenish blue Freshly prepared with0.28 Pale blue hydrochloric acid 0.56 Blue 0.84 Deep blue 5-day oldsolution with no 0.28 Pale dark green acid 0.56 Dark green 0.84 Deepdark green 5-day old solution with 0.28 Pale blue hydrochloric acid 0.56Blue 0.84 Deep blue

[0068] From Table 2, it can be seen that, by adding hydrochloric acid tothe ferric chloride solution, the reacted solution can display differentshades of color. Moreover, with the added acid, the ferric chloridesolution was stabilized to pale yellow color, and thus the resultingreacted solution displayed a consistent hue of blue independent of theaging time. This method can be used, in particular for semi-quantitativetest, to stabilize the color of the ferric chloride solution such that aconsistent hue of color could be obtained at the end of test forcomparing with a color correlation chart.

EXAMPLE 4

[0069] This example describes a method, based on the AA indicatordeveloped in this invention, for detecting AA in PET preforms. In aproduction setting, typically, preforms are sampled at a predeterminedtime interval to ensure that the AA levels are within specification. Toillustrate how the current invention can be used for detecting AA levelsin preforms, preforms were made using different injection molding cycletimes to give preforms of five different AA levels.

[0070] The preforms were purged with a clean stream of nitrogen to avoidthe possible contamination of AA from the air in the injection moldingproduction environment. An indicator strip, produced as described inEXAMPLE 1, was placed in each of the preforms, and capped to form ahermetic headspace in the preform as shown in (FIG. 2). Referring toFIG. 4, the capped preforms were then placed upright on a stainlesssteel lid 22 equipped with holes, such that the neck support ledge 24 ofthe preforms was resting on the lid. The preforms were then submerged ina thermostated water bath 26 containing heated water 28 equilibrated at90° C., to a water level 30 just below the neck support ledge region toavoid deforming the closure. The preforms were positioned so thatsufficient spacing was available for the heated fluid to circulatefreely through the bath to achieve even heating for all preforms. Thepreforms were allowed to heat in the water bath for one hour to allow AAto diffuse into the headspace. After heating, the preforms were removedfrom the water bath and the individual test strip, which had beenreacted with AA in the preform headspace during heating, was removed anddipped in 0.8 mL freshly prepared 0.63% (w/v) ferric chloride solutioncontained in a disposable polystyrene cuvet. A second unreacted teststrip was also added to the ferric chloride solution to ensure that anexcess MBTH was available for reaction. The strips were allowed to reactin the ferric chloride solution for 30 min with occasional swirling. Theabsorbance values of the resulting solutions were determined using aspectrophotometer at 600 nm wavelength. Calibration of thespectrophotometer was carried out by testing the indicator strips underthe same conditions in empty glass vials that has been dosed with knownamounts of AA standard.

[0071] To correlate the result with the conventional GPAA value, asecond set of preforms, produced under the exact conditions as per theaforementioned preform molding cycles, were tested according to the GPAAtest protocols. The preforms were first cooled in liquid nitrogen andground in a mill to form a powder. The powder was sieved through 1 mmsize sieve and then weighed accurately (0.25 g) into an airtight 22 mLheadspace vial. The vial was capped and heated to 145° C. for 60 min inan autosampler (HP7694 Headspace Sampler, Agilent Technologies, Inc.,Wilmington, Del.) coupled to a gas chromatograph (6850 Series GC System,Agilent Technologies, Inc., Wilmington, Del.). Following the heatingprocess, the AA diffused into the vial headspace was sampled andanalyzed by the GC. Calibration of the GC response was done by injectingknown amounts of AA standard to the headspace vial and testing the vialsunder the same conditions as per the grind samples.

[0072] As shown in FIG. 5, a strong linear correlation exists betweenthe two tests with a coefficient of determination of >0.98. This showsthat by using the indicator strip in conjunction with the aforementionedpreform headspace method, it is possible to predict the GPAA valueaccurately without carrying out the GPAA procedure. Once the correlationrelationship (similar to FIG. 5) is established, the indicator can beused for monitoring the AA level in preforms during production. Forinstance, if 2.5 μg of AA were found to be reacted with the indicator,based on the correlation plot in FIG. 5, the preform would contain anequivalent amount of 13 ppm of AA if the test were to be tested usingthe ground parison procedure. It is noteworthy that, unlike the groundparison procedure, the amount of AA detected by the current indicatormethod, thus the relationship shown in FIG. 5, depends on the size andshape of the preform. By normalizing the results to unit inner surfacearea of the preform, it may possible to derive a generic correlationthat can be used for correlating the AA data for preforms of varioussizes.

[0073] It is to be understood that the invention is not limited to theillustrations described herein, which are deemed to illustrate the bestmodes of carrying out the invention. From the foregoing description, oneskilled in the art can readily ascertain the essential characteristicsof this invention and make various changes and modifications of theinvention to adapt it to various usages and conditions without departingfrom the spirit and scope as defined by the claims.

What is claimed is:
 1. A method for measuring aldehyde present in apolymer, comprising the steps of: (a) extracting gaseous aldehyde from apolymer into a confined space; (b) reacting said gaseous aldehyde withan aldehyde-reactive reagent on a reagent carrier in said confinedspace; (c) contacting said aldehyde-reactive reagent with a reagentsolution to obtain a detectable response; and (d) measuring a responseto obtain an aldehyde reading.
 2. The method of claim 1, wherein saidextracting step further includes a step of raising the temperature ofsaid polymer.
 3. The method of claim 1, further including the step ofagitating said reagent solution for reducing the duration of saidcontacting step.
 4. The method of claim 1, further including the step ofheating said reagent solution for reducing the duration of saidcontacting step.
 5. The method of claim 1, wherein said measuring stepis a visual comparison of said response with a chart.
 6. The method ofclaim 1, wherein said measuring step includes a photometric instrumentfor measuring said response.
 7. The method of claim 1, wherein saidmeasuring step is conducted using a transmission mode.
 8. The method ofclaim 1, wherein said measuring step is conducted using a reflectancemode.
 9. The method of claim 1, wherein said reagent solution is presentin excess quantity for dissolving said reacted aldehyde-reactive reagentfor forming a homogeneous solution.
 10. The method of claim 1, whereinsaid confined space is an airtight container, said polymer disposed insaid container.
 11. The method of claim 1, wherein said confined spaceis formed by the combination of a preform and closure.
 12. The method ofclaim 1, wherein said confined space is formed by the combination of abottle and closure.
 13. The method of claim 1, wherein said polymer is apreform.
 14. The method of claim 1, wherein said polymer is a bottle.15. The method of claim 1, 14, 15 wherein said polymer is in pieces. 16.The method of claim 1, wherein said aldehyde-reactive reagent comprisesa compound selected from the group consisting of3-methyl-2-benzothiazolinone hydrazone hydrochloride,4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, 2-hydrazinobenzothiazole,2,4-dinitrophenylhydrazone, 5-dimethylaminonaphthalene-1-sulfohydrazide,2-diphenylacetyl-1,3-indandione-1-hydrazone,2-hydrazinobenzothiazole-4-nitrobenzenediazonium fluoborate,p-nitrobenzalhydrazone, 1,3-cyclohexanedione, 3,5-diaminobenzoic acid,5,5-dimethylcyclohexane-1,3-dione, 2-hydroxycarbazole, dimedone andindole.
 17. A method for measuring acetaldehyde present in a polyesterpolymer, comprising the steps of: (a) extracting gaseous acetaldehydefrom a polymer into a confined space; (b) reacting said gaseousacetaldehyde with an aldehyde-reactive reagent disposed on an indicatorin said confined space; (c) contacting the aldehyde-reactive reagentwith an oxidizer solution to obtain a color change in said oxidizersolution; and (d) measuring the color response to obtain an acetaldehydereading.
 18. The method of claim 17, wherein said extracting stepfurther includes a step of raising the temperature of said polymer. 19.The method of claim 17, further including the step of agitating saidreagent solution for reducing the duration of said contracting step. 20.The method of claim 17, further including the step of heating saidreagent solution for reducing the duration of said contracting step. 21.The method of claim 17, wherein said measuring step is a visualcomparison of said response to a chart.
 22. The method of claim 17,wherein said measuring step is conducted with a spectrophotometer. 23.The method of claim 17, wherein said confined space is an airtightcontainer, said polymer disposed within said container
 24. The method ofclaim 17, wherein said confined space is formed by the combination of apreform and closure.
 25. The method of claim 17, wherein said confinedspace is formed by the combination of a bottle and closure.
 26. Themethod of claim 17, wherein said polymer is a preform.
 27. The method ofclaim 17, wherein said polymer is a bottle.
 28. The method of claim 17,26, or 27, wherein said polymer is in pieces.
 29. The method of claim17, wherein said aldehyde-reactive reagent is3-methyl-2-benzothiazolinone hydrazone hydrochloride.
 30. The method ofclaim 17, wherein said indicator comprises an aldehyde-reactive reagentcoated on a solid particulate carrier applied to a support strip. 31.The method of claim 17, wherein said oxidizer solution is an aqueoussolution of ferric chloride.
 32. The method of claim 17, wherein saidoxidizer solution is an aqueous solution of potassium ferricyanide. 33.The method of claim 17, wherein said oxidizer solution is an aqueoussolution of lead tetraacetate.
 34. The method of claim 17, wherein saidoxidizer solution is an aqueous solution of periodic acid.
 35. A methodof making an indicator for testing aldehyde in polymer, comprising thesteps of: (a) contacting a solution of aldehyde-reactive reagent with acarrier; and (b) drying the reagent in an atmosphere non-reactive withsaid reagent to form an aldehyde-reactive reagent coated carrier. 36.The method of claim 35 further including the step of applying saidcoated carrier to a support.
 37. The method of claim 36 wherein thesolvent for forming said solution is water.
 38. The method of claim 36wherein the solvent for forming said solution is an organic solvent. 39.The method of claim 36 wherein the pH of said solution is optimized topromote solubilization of said aldehyde-reactive reagent.
 40. The methodof claim 36 wherein said carrier is a plurality of particles.
 41. Themethod of claim 36 wherein said carrier is a plurality of beads.
 42. Themethod of claim 36 wherein said carrier is a film.
 43. The method ofclaim 36 wherein said carrier is a membrane.
 44. The method of claim 36wherein said carrier is a fiber.
 45. The method of claim 36 wherein saidcarrier is a sheet.
 46. The method of claim 36 wherein said carrier is afoam.
 47. The method of claim 36 wherein said carrier is alumina. 48.The method of claim 36 wherein said carrier is a silaca gel.
 49. Themethod of claim 36 wherein said carrier is glass.
 50. The method ofclaim 36 wherein said carrier is kaolin.
 51. The method of claim 36wherein said carrier is diatomaceous earth.
 52. The method of claim 36wherein said carrier is ceramic.
 53. The carrier of claim 36 whereinsaid carrier is a synthetic polymer.
 54. The method of claim 36 whereinsaid drying step is conducted with heat.
 55. The method of claim 54wherein said heat is supplied by a vacuum oven.
 56. The method of claim54 wherein said heat is supplied by a water bath.
 57. The method ofclaim 54 wherein said heat is supplied by a heater tape.
 58. The methodof claim 54 wherein said heat is supplied by a heater mantle.
 59. Themethod of claim 54 wherein said heat is supplied by a heater block. 60.The method of claim 54 wherein said heat is supplied by an infraredlamp.
 61. The method of claim 54 wherein said heat is supplied by amicrowave.
 62. The method of claim 36 wherein said atmosphere isprovided by a vacuum.
 63. The method of claim 36 wherein said atmosphereis provided by a continuous flow of a dry non-reactive gas.
 64. Themethod of claim 36 wherein said carrier and said support are inert tosaid aldehyde-reactive reagent.
 65. The method of claim 36 wherein saidcarrier is adhesively bonded to said support.
 66. The method of claim 36wherein said carrier is physically immobilized to said support.
 67. Themethod of claim 36 wherein said carrier is a support.
 68. A method ofmaking an indicator for testing acetaldehyde in polyester polymer,comprising the steps of: (a) contacting a solution of aldehyde-reactivereagent with a particulate carrier; (b) drying the reagent coatedparticulate carrier in an atmosphere non-reactive with said reagent toform aldehyde-reactive reagent coated carrier; (c) applying a thin layerof the coated particulate carrier to an adhesive tape inert to saidreagent; (d) bonding said tape to a support.
 69. The method of claim 68wherein said tape is single sided.
 70. The method of claim 68 whereinsaid tape is double sided.
 71. The method of claim 68, 69, or 70 whereinsaid tape covers a portion of said support.
 72. The method of claim 68wherein said solution is prepared by dissolving3-methyl-2-benzothiazoline hydrazone hydrochloride hydrate in water. 73.The method of claim 72 wherein the concentration of said3-methyl-2-benzothiazoline hydrazone hydrochloride solution is between0.5 to 3% by weight.
 74. The method of claim 68 wherein said particulatecarrier comprises alumina.
 75. The method claim 74 wherein said aluminais less than 180 μm in size.
 76. The method of claim 68 wherein saidindicator includes a detection limit of at least 0.5 μg of acetaldehyde.77. The method of claim 68 wherein said drying step is conducted in heatand a vacuum.
 78. A kit for measuring aldehyde in a polymer, comprising:(a) at least one seal for forming an airtight confined space, (b) analdehyde-reactive reagent coated carrier on a support, and (c) a reagentsolution.
 79. A kit as in claim 78 wherein said seal is a closuresuitable for forming an airtight confined space within a molded part tocontain aldehyde extracted from said polymer..
 80. A kit as in claim 78wherein said seal is a container suitable for forming an airtightconfined space around a molded part to contain aldehyde extracted fromsaid polymer.
 81. The kit as in claim 78 wherein said kit furtherincludes a closure equipped with a septa for sealing a molded part, andan air-tight syringe to sample headspace gas from said confined space.82. The kit as in claim 78 wherein said kit further includes a chart fordetermining the amount of reacted aldehyde.
 83. The kit as in claim 78wherein said kit further includes a spectrophotometer for determiningthe amount of reacted aldehyde.
 84. The kit as in claim 78 wherein saidkit further includes a correlation table for correlating the aldehydedetected with the aldehyde content of said polymer.
 85. The kit as inclaim 78 wherein said carrier is a plurality of particles.
 86. The kitas in claim 78 wherein said carrier is a plurality of beads.
 87. The kitas in claim 78 wherein said carrier is a film.
 88. The kit as in claim78 wherein said carrier is a membrane.
 89. The kit as in claim 78wherein said carrier is a fiber.
 90. The kit as in claim 78 wherein saidcarrier is a sheet.
 91. The kit as in claim 78 wherein said carrier isfoam.
 92. The kit as in claim 78 wherein said carrier and said supportare disposed in a sealed package.
 93. The kit as in claim 92 whereinsaid package is moisture and light resistant.
 94. The kit as in claim 78further including a fiber coated with an aldehyde-reactive reagenthoused within a needle of a syringe.
 95. The kit as in claim 78 whereinsaid aldehyde-sensitive reagent is 3-methyl-2-benzothiazolinonehydrazone hydrochloride.
 96. The kit as in claim 78 wherein said reagentsolution reacts with said aldehyde-reactive reagent providing adetectable response.
 97. The kit as in claim 78 wherein said reagentsolution is an aqueous solution of ferric chloride.
 98. The kit as inclaim 78 wherein said reagent solution is an aqueous solution ofpotassium ferricyanide.
 99. The kit as in claim 78 wherein said reagentsolution is an aqueous solution of lead tetraacetate.
 100. The kit as inclaim 78 wherein said reagent solution is an aqueous solution ofperiodic acid.
 101. The kit as in claim 78 wherein said reagent solutionis an acidified ferric chloride solution.
 102. The kit as in claim 101wherein said the concentration of said ferric chloride solution isbetween 0.5 to 3% by weight.
 103. The kit as in claim 78, wherein saidaldehyde-reactive reagent is selected from the group consisting of3-methyl-2-benzothiazolinone hydrazone hydrochloride,4-amino-3-hydrazino-5-mercapto-1,2,4-triazole, 2-hydrazinobenzothiazole,2,4-dinitrophenylhydrazone, 5-dimethylaminonaphthalene-1-sulfohydrazide,2-diphenylacetyl-1,3-indandione-1-hydrazone, 2-hydrazinobenzothiazole-4-nitrobenzenediazonium fluoborate, p-nitrobenzalhydrazone,1,3-cyclohexanedione, 3,5-diaminobenzoic acid,5,5-dimethylcyclohexane-1,3-dione, 2-hydroxycarbazole, dimedone andindole.